Overhead doors have been used on loading docks and in various other warehouse and factory settings for many years. Conventional overhead doors are of the sectional type, and typically include four or more rectangular panels hinged together along the upper and lower edges. Each of the door panels carries two guide assemblies near the upper hinge line, and the bottom door panel carries two additional guide assemblies near the bottom edge. Each of the guide assemblies typically includes a plunger or roller device that extends outwardly from the door panel and is movably received in a channel section of an adjacent door track. The door tracks extend along the left and right sides of the door, and guide the door as it moves upwardly into the overhead or “open” position.
Many overhead doors include spacers between the door panels for sealing and other reasons. Because the pivot axes of the panel hinges are not collinear with the guide plunger axes, the panel spacers can prevent adjacent door panels from back-bending. This can lead to binding as the door is moved upwardly on curved guide tracks.
Another problem with conventional overhead doors is that they are susceptible to damage when used in factories, warehouses, and other commercial and industrial settings. Occasionally, for example, a forklift operator may inadvertently run into the door, as can happen when the door is in a partially open position. This can damage the door and/or the door tracks, making further use of the door difficult or impossible without time-consuming repairs. One way to overcome this problem is to equip the door with spring-loaded guide assemblies that retract and release from the tracks when struck with sufficient force in one or more directions, as disclosed in, for example, U.S. Pat. No. 5,535,805 to Kellog, et al., U.S. Pat. No. 5,927,368 to Rohrer, et al., U.S. Pat. No. 6,041,844 to Kellog, et al., U.S. Pat. No. 6,095,229 to Kellog, et al., U.S. Pat. No. 6,119,307 to Weishar, et al., and U.S. Pat. No. 6,273,175 to Kellog, et al. (All of the foregoing patents are incorporated into the present disclosure in their entireties by reference).
Although configuring the door to release in one or both directions may avoid damage to the door when struck, this approach can present additional problems. For example, under certain conditions the entire door could be knocked out of the tracks, and reinstalling an entire door can be a difficult and time-consuming task. Furthermore, one or more spreader bars may be necessary to help hold the overhead door tracks in position.